Over 25 years ago I built Rotodyne for two .45 glow engines. I think, the diameter of the rotor was approximately 60”. The rotor head did tilt back, but not enough for proper autorotation. The restriction on the tilt angle were these two vertical fins at the tips of stabilizer. At that time I did not know that on the full size plane, they were tilted to almost horizontal position when taking off or landing. I remember running the model up and down the runway at high speeds. The rotor was spinning but not fast enough and the stubby wing was not producing enough lift for the model with relatively high wing loading.